1. Field of the Invention
The present invention relates, in general, to speed detection of moving vehicles, and more particularly to compact, mobile speed detection systems that provide for accurate speed detection with accompanying image capture, processing, and production at the location of the field portion of the system, such as the present location of the law enforcement vehicle.
2. Relevant Background
Law enforcement agencies and personnel presently use a variety of speed measurement devices to monitor traffic and, more particularly, to identify vehicles that are going faster than posted speed limits. In addition to identifying a speeding vehicle, it has become increasingly common to attempt to capture images of such speeding vehicles and then to use the images to better enforce the speed limits (i.e., use the image as part of a ticketing program). While satisfying some of the needs of the law enforcement agencies, the existing speed measurement and image capture devices have not proven suitable or reliable for many law enforcement agency applications and have created operational problems that hinder the field use of such devices.
Various methods are used to detect the speed of moving vehicles, such as well-known radar systems. More recently, speed detection systems have incorporated lasers to accurately detect the speed of a moving vehicle and also the distance or range of the vehicle from the laser device. In general, laser speed detectors measure the time delay between the transmission of a series of pulses and a reflection of those pulses. The design and operation of laser speed detection and range finder systems may be found in U.S. Pat. No. 5,359,404 entitled xe2x80x9cLaser-Based Speed Measuring Device, U.S. Pat. No. 5,652,651 entitled xe2x80x9cLaser Range Finder Having Selectable Target Acquisition Characteristics and Range Measuring Precisionxe2x80x9d, and U.S. Pat. No. 6,057,910 entitled xe2x80x9cSelf-Calibrating Precision Timing Circuit and Method for Laser Range Finderxe2x80x9d, which are each incorporated herein by reference. Typically, these laser speed detection systems provide accurate measures of a vehicle""s speed and are useful for providing onsite speed measurements, e.g., at the location of a law enforcement vehicle, that could then be entered on a ticket by law enforcement personnel.
Improvements have been made to increase the accuracy and usefulness of these laser-based speed detection systems. For example, U.S. Pat. No. 5,938,717 entitled xe2x80x9cSpeed Detection and Image Capture System for Moving Vehiclesxe2x80x9d, which is incorporated herein by reference, discloses a system for accurately aligning a laser speed detector and for capturing an image of a speeding vehicle with a video camera. The system also provides the advantage of automating the capture of images of speeding vehicles at a predetermined distance from the system and of capturing a set of useful information (e.g., date, time, location, speed limit, detected speed, and the like). A computer system is included in the disclosed system to run a frame grabber program to capture a frame of the video image. The computer system includes a removable data storage device for storing the captured image frames and the associated set of information.
Generally, the system is taught to be operated by placing the system in a selected location to monitor vehicle speeds, such as along a road with the bulky computer system position in the back of a van or other vehicle. The system is initially set up by an operator and then allowed to operate automatically without or with minimal operator control for a certain period of time. An operator then removes the data storage device from the system and takes the data storage device back to a separate office or facility for processing of the captured images (i.e., grabbing a still image from the video) and data with a computer system at the office. In this manner, tickets can be produced by combining the video image with the collected data and then mailing the ticket to owners of vehicles that violated a speed limit by a selected amount (such as 5 miles per hour in a school zone and 10 miles per hour for a highway). A hardcopy of the image may be included with the ticket with the data being overlaid by the office computer system. In some applications, the field computer system, such as a personal computer, includes a monitor to allow an operator to view the collected image and to facilitate entering of field parameters. Additionally, the field computer system may perform some of the processing features (such as overlaying of the set of information on a grabbed frame of the video) and may include a thermal printer to produce copies of the image with the overlaid information at the field unit.
While addressing some of the needs of law enforcement agencies, the video-based laser speed detection systems have not addressed all of the operating problems facing field operators and are not particularly useful in some field applications. For example, the use of frame grabbing with a video camera for image capturing is most effective with a relatively high capacity and higher speed data processing system and large data storage capacity. Typically, the computer requirements are met with a personal computer with central processing unit with a frame grabber PC card installed and associated monitor and keyboard. The combined use of a video camera with a personal computer results in a bulky package that is often costly and is usually physically large, which limits its usefulness in the field. It is not convenient or even practical for a single operator, i.e., law enforcement officer, to quickly deploy the system and then periodically move the entire system or portions of the system without moving the whole vehicle in which the system is positioned. The portability of these video-based systems is further limited by the need for a large number of communication cables and power cords (e.g., generally AC and DC power provided to each component) between the various components.
One of the most significant advantages of a laser-based speed measurement instrument is its ability to narrowly target a single car within a group of cars. However, there is still a need for proof that the detected speed is matched with the correct car. This proof can be provided with the overlaid information if it is accurately synchronized with the proper, grabbed video frame. Of course, this synchronization and combining of information requires additional processing capacity that increases the cost and sometimes the size of the system. Also, the time required to process the information and to print out a hard copy of the produced image limits its desirability as evidence or proof of speeding in the field as enforcement officers demand relatively quick to support the issuance of a speeding ticket.
Hence, there remains a need for a device or system for detecting a speed of a moving vehicle and for capturing an image of the vehicle that provides an accurate determination of the vehicle""s speed along with readily accessible proof that the speed has been correctly matched to the proper vehicle. Preferably, such a speed measurement device would be designed for field use (such as inside or outside an operator""s vehicle) providing prompt and useful evidence of a vehicle""s speed while also being compact, lightweight, and easy to operate. The device would also preferably be useful in various weather conditions, provide protection of collected images and data, and be relatively inexpensive to purchase and operate.
The present invention addresses the above discussed and additional problems by providing a compact and portable speed measurement and image capture system that combines an accurate laser speed detector with a programmable digital camera and a portable field processor. The portable field processor is configured to allow an operator to enter capture session and system parameters, such as a posted speed limit and a capture speed level, and to receive vehicle speed signals from the speed detector. The portable field processor operates to selectively transmit image capture signals to the digital camera in response to these speed signals (e.g., generates image capture signals when the capture speed level is exceeded). The digital camera is programmed to retrieve a still image of the vehicle from its buffers or memory and create and transmit a digital image file (such as a file compressed per JPEG standards). The portable field processor then writes the speed signal data into the digital image file and displays the combined file on a display screen. The portable field processor can then be detached from the system by a field operator to show the displayed image to a vehicle operator. In one embodiment, a classification sensor is provided to detect whether the vehicle is a commercial vehicle, such as by height measurements, axle counting, weight measurements, and the like, and two distinct capture speed levels are used to effectively capture images of private and commercial speeding vehicles that may different speed limits.
According to one aspect of the invention, a compact speed measurement system is provided for field or onsite use in measuring speeds of vehicles and capturing images of select vehicles. The system includes a laser-based speed detector for determining a speed of a vehicle in a specific target area. When a speed is determined, the detector generates a speed signal. The system also includes a camera generally aligned with the speed detector operable to capture and store digital-format still images of vehicles in memory. Specifically, the camera is programmed to respond to an image capture signal to generate and transmit a digital image file including a still image of the vehicle targeted by the detector. A portable field processor is communicatively linked to the speed detector and the camera to first receive the speed signal, to process the speed signal and in response transmit an image capture signal to the camera, and to receive the digital image file from the camera.
In a preferred embodiment, the portable field processor includes software to create a combined speed and image data file by modifying the digital image file to include speed data from the speed signal. For example, the digital image file may be a JPEG-format file and the modifying may involve writing the speed data to the header of the JPEG file. The portable field processor includes a display screen and is configured to display the modified digital image file on the display screen. An operator can then operate the field processor to enlarge and/or enhance selected portions of the displayed image (such as to enlarge the license plate portion of the image). The field processor can be readily detached from the system and hand carried to a stopped vehicle to show the vehicle operator the displayed image as proof of their speed. To control the risk of data loss, the system is configured such that the digital camera acts as a charging power source for the field processor, i.e., the camera will stop operating before the field processor loses power thus assuring storage of all captured images.
According to another aspect of the invention, a method is provided for measuring a speed of a moving vehicle and capturing a digital image of the same moving vehicle. The method involves initially positioning and setting up a speed detector and a camera at a location selected by an operator for targeting vehicles moving through a target area. The camera is operated on an ongoing basis to capture or temporarily store a still image of each vehicle passing through the target area. The speed detector operates on an ongoing basis to determine the speed of a specific vehicle in the target area. The speed data including the determined speed is transmitted to a portable field processor. The speed data is processed by the field processor, which responds by transmitting a trigger signal to the camera. The camera receives the trigger signal, responds by retrieving a still image corresponding to the targeted vehicle, and then transmits the still image in a digital image file to the portable field processor.
In one embodiment of the method, several of the functions are synchronized to insure that the captured image is an image of the same moving vehicle that was targeted by the speed detector. This is achieved by determining the speed at a speed measurement time with the detector and operating the camera to store still images during an image timing cycle. Synchronization occurs by operating the field processor to transmit the trigger signal within the timing cycle that also coincides with the speed measurement time.
In another embodiment of the method, the method includes determining the classification of the vehicle, such as with a separate classification sensor (e.g., a height sensor). The classifications may include private or lower weight vehicles, commercial trucks or higher weight vehicles, and other classifications that may be used by governments in establishing differing speed limits (e.g., 55 mph for commercial vehicles and 65 mph for private vehicles). In this embodiment, the processing of the speed data includes first identifying the classification of the vehicle (such as from the combined speed data string including vehicle speed, range of vehicle from speed detector, and the vehicle type) and then comparing the detected speed with the speed limit for that type of vehicle. Vehicle classification in the method may be achieved in many ways. For example, vehicle classification may include sending a signal directly to the field processor from a separate sensor configured to detect vehicle type or classification may include concatenating vehicle type information onto the laser speed detector data string.